As a distillation column having an excellent energy-saving property, an internal heat exchanging type distillation column which includes a low-pressure column and a high-pressure column is configured so as to exchange heat between both the columns, and does not require transfer of heat with others is known.
Also, an internal heat exchanging type distillation column which relates to the above internal heat exchanging type distillation column, and is configured such that heat is made to transfer from the high-pressure side inside a pipe which is filled with a regular filler to the low-pressure side inside a pipe which is similarly filled with a regular filler, whereby the high-pressure side inside the pipe functions as an enriching section and the low-pressure side outside the pipe functions as a stripping section is suggested (refer to Patent Document 1).
That is, this internal heat exchanging type distillation column, as shown in FIG. 9, includes a body barrel 51, a plurality of pipes 75 that is inserted into the body barrel 51, and an upper pipe plate 53a and a lower pipe plate 53b that connect the plurality of pipes 75 to the body barrel 51. Also, the internal heat exchanging type distillation column has a structure in which a pipe inside 54 and a pipe outside 55 of each pipe 75 are separated from each other, and is configured such that the pipe inside 54 functions as an enriching section on the high-pressure side, and the pipe outside 55 functions as a stripping section on the low-pressure side.
Additionally, a stripping section liquid inlet 56 for supplying liquid to the pipe outside (stripping section) 55 and a stripping section steam outlet 57 which allows steam from the pipe outside (stripping section) 55 to be extracted therethrough are disposed in an upper portion of the body barrel 51, and an enriching section liquid inlet 58 for supplying liquid to the pipe inside (enriching section) 54 and an enriching section steam outlet 59 which allows the steam from the pipe inside (enriching section) 54 to be extracted therethrough are disposed in an end chamber 64a which communicates with the pipe inside (enriching section) 54 above the upper pipe plate 53a. 
On the other hand, a stripping section steam inlet 60 for supplying steam to the pipe outside (stripping section) 55 and a stripping section liquid outlet 61 which allows the liquid from the pipe outside (stripping section) 55 to be extracted therethrough are disposed in a lower portion of the body barrel 51, and an enriching section steam inlet 62 for supplying steam to the pipe inside (enriching section) 54 and an enriching section liquid outlet 63 which allows the liquid from the pipe inside (enriching section) 54 to be extracted therethrough are disposed in an end chamber 64b which communicates with the pipe inside (enriching section) 54 below the lower pipe plate 53b. Additionally, the pipe inside (enriching section) 54 and the pipe outside (stripping section) 55 are filled with fillers (regular filler) 54a and 55a. 
Additionally, in this internal heat exchanging type distillation column, as shown in FIG. 10, a plurality of single pipe units 80 having a structure in which the filler layer (regular filler) 55a is disposed so as to surround an outer peripheral surface of the pipe 75, and the filler layer 55a disposed at the outer peripheral surface of the pipe 75 is covered with a partition pipe 65 made of a metallic thin plate are disposed at a predetermined pitch inside the body barrel 51, whereby the pipe inside 54 and the pipe outside 55 of each pipe 75 are isolated from each other inside the body barrel 51, and the filler layer 55a is disposed around each pipe 75.
According to the internal heat exchanging type distillation column of this Patent Document 1, it is possible to realize a high energy-saving property and excellent distillation performance simultaneously.
Meanwhile, in the internal heat exchanging type distillation column configured as described above, cleaning of a distillation section, such as a pipe inside or a pipe outside may be required by continuous operation. In this case, although it is desirable to extract and clean a distillation section composed of the pipe 75, the regular fillers 54a and 55a disposed at the pipe inside 54 and the pipe outside 55, respectively, and the like from the body barrel, it is not necessarily easy to extract the distillation section from the body barrel. Therefore, a method, such as chemical cleaning, which performs cleaning without disassembling an apparatus, is considered. In this case, even when sufficient cleaning cannot be necessarily performed, there is a problem in that replacement or the like of filler cannot be performed, and sufficient performance cannot be recovered.
Meanwhile, in the internal heat exchanging type distillation column, a raw material liquid is supplied to an uppermost portion on the side of a stripping section and the liquid flows down to a lowermost portion of the stripping section, and an enriching section is supplied with steam without any soiling from the stripping section. Therefore, it is a situation in which the degree of soiling is apt to become stronger at the pipe outside 55 on the side of the stripping section than the pipe inside 54 on the side of the enriching section.
Thus, it is suggested that the pipe outside on the side of the stripping section where the degree of soiling is apt to become stronger has a wet wall structure in which cleaning is relatively easy (refer to Patent Document 2).
However, the internal heat exchanging type distillation column has advantages in using a filler for the distillation section. For example, the filler has a large number of theoretical stages per unit height compared to a wet wall or a shelf stage. In a packed column, compared to a wet wall column or a shelf stage column, the height of the column can be designed low, the space of a facility can be reduced, and the cost can be reduced.
Thus, in order to make the internal heat exchanging type distillation column of a packed column type more significant, it is necessary to enable the distillation section to be extracted, and thus to enable performance to be reliably recovered even when the distillation section is soiled.
However, as described above, in the present circumstances, it is a situation in which the distillation section, especially, the filler of the stripping section is not easily extracted.    Patent Document 1: Unexamined Japanese Patent Application, First Publication No. 2004-016929    Patent Document 2: Unexamined Japanese Patent Application, First Publication No. 2004-037017